Vitamin A deficiency

What does this indicator tell us?

Vitamin A deficiency results from a dietary intake of vitamin A that is inadequate to satisfy physiological needs. It may be exacerbated by high rates of infection, especially diarrhoea and measles. It is common in developing countries, but rarely seen in developed countries. Vitamin A deficiency is a public health problem in more than half of all countries, especially those in Africa and South-East Asia. The most severe effects of this deficiency are seen in young children and pregnant women in low-income countries.

How is it defined?

Vitamin A deficiency can be defined clinically or subclinically. Xerophthalmia is the clinical spectrum of ocular manifestations of vitamin A deficiency; these range from the milder stages of night blindness and Bitot spots to the potentially blinding stages of corneal xerosis, ulceration and necrosis (keratomalacia). The various stages of xerophthalmia are regarded both as disorders and clinical indicators of vitamin A deficiency. Night blindness (in which it is difficult or impossible to see in relatively low light) is one of the clinical signs of vitamin A deficiency, and is common during pregnancy in developing countries. Retinol is the main circulating form of vitamin A in blood and plasma. Serum retinol levels reflect liver vitamin A stores when they are severely depleted or extremely high; however, between these extremes, plasma or serum retinol is homeostatically controlled and hence may not correlate well with vitamin A intake. Therefore, serum retinol is best used for the assessment of subclinical vitamin A deficiency in a population (not in an individual). Blood concentrations of retinol in plasma or serum are used to assess subclinical vitamin A deficiency. A plasma or serum retinol concentration <0.70 μmol/L indicates subclinical vitamin A deficiency in children and adults, and a concentration of <0.35 µmol/L indicates severe vitamin A deficiency.

What are the consequences and implications?

Night blindness is one of the first signs of vitamin A deficiency. In its more severe forms, vitamin A deficiency contributes to blindness by making the cornea very dry, thus damaging the retina and cornea. An estimated 250 000–500 000 children who are vitamin A-deficient become blind every year, and half of them die within 12 months of losing their sight. Deficiency of vitamin A is associated with significant morbidity and mortality from common childhood infections, and is the world’s leading preventable cause of childhood blindness. Vitamin A deficiency also contributes to maternal mortality and other poor outcomes of pregnancy and lactation. It also diminishes the ability to fight infections. Even mild, subclinical deficiency can be a problem, because it may increase children's risk for respiratory and diarrhoeal infections, decrease growth rates, slow bone development and decrease the likelihood of survival from serious illness.

Cut-off values for public health significance

Reference: WHO, 2009.

Source of data

WHO. Vitamin and Mineral Nutrition Information System (VMNIS). Micronutrients database. (http://www.who.int/vmnis/database/en/).

Further reading

Stevens GA, Bennett JE, Hennocq Q, Lu Y, De-Regil LM, Rogers L et al. Trends and mortality effects of vitamin A deficiency in children in 138 low-income and middle-income countries between 1991 and 2013: a pooled analysis of population-based surveys. Lancet Glob Health. 2015;3:e528–36. doi:10.1016/S2214-109X(15)00039-X.

WHO. Global prevalence of vitamin A deficiency in populations at risk 1995-2005. WHO global database on vitamin A deficiency. Geneva: World Health Organization; 2009 (http://whqlibdoc.who.int/publications/2009/9789241598019_eng.pdf).

WHO. Serum retinol concentrations for determining the prevalence of vitamin A deficiency in populations. WHO/NMH/NHD/MNM/11.3. Geneva: World Health Organization; 2011 (http://www.who.int/vmnis/indicators/retinol.pdf).

WHO. Xerophthalmia and night blindness for the assessment of clinical vitamin A deficiency in individuals and populations. WHO/NMH/NHD/EPG/14.4. Geneva: World Health Organization; 2014 (http://apps.who.int/iris/bitstream/10665/133705/1/WHO_NMH_NHD_EPG_14.4_eng.pdf).

Internet resources

WHO. Vitamin A deficiency list of publications. (http://www.who.int/nutrition/publications/micronutrients/vitamin_a_deficiency/en/).

WHO. e-Library of Evidence for Nutrition Actions (eLENA). Nutrients. Vitamin A. (http://www.who.int/elena/nutrient/en/#vitamina).